Well if Andy ever retires I don't see many guys at 185 who could even give Machida a run for his money. He is actually a terrible matchup for most of the top of the division.
Vitor V Lyoto would be a good fight, Weidman also. I think the next MW champion will be Rory Mac though. Weidman will go to 205 after he recovers from the beating that Anderson will give him.